Fire Alarm Interfaces

Overview

Interfaces (also called I/O units or modules) provide the link between the fire alarm system and external equipment. They are essential for implementing cause & effect strategies, such as releasing doors, shutting down ventilation, or initiating smoke control.

BS 5839-1:2025 (Clause 8) recognises that fire alarm systems can actuate other fire protection systems or safety facilities for life safety, property protection, or both, provided this interconnection does not prejudice system reliability.

Types of Interfaces

Type	Function	Typical Examples
Input Modules	Monitor a signal or contact from external equipment.	Sprinkler flow switch, plant shutdown feedback, door contact.
Output Modules	Provide a relay or voltage output to trigger external equipment.	Releasing maglocks, fan start, damper closure.
I/O Modules	Combined input and output in a single device.	Firefighter’s lift control, smoke vent with position feedback.
Sounder/Beacon Controllers	Addressable control of notification appliances.	Localised evacuation, phased evacuation.
Protocol Gateways	Convert fire panel signals into third-party protocols.	Modbus, BACnet, ONVIF, BMS integration.

Common Applications

Access Control: Release of electromagnetic locks, as required by BS 7273-4.
HVAC & Plant: Stopping fans, closing dampers, or isolating fuel valves.
Smoke Control: Starting AOVs, initiating mechanical extract, interfacing with smoke control panels.
Lifts: Recall/grounding of lifts or enabling firefighter’s override.
Sprinkler Systems: Monitoring flow and tamper switches, transmitting alarms.
Suppression Systems: Gas release or fire curtain deployment (with dual-signal safeguards).

Technical Considerations (per BS 5839-1:2025)

Compliance with BS 7273: All relevant recommendations for door release, smoke control, and other safety functions must be met.
Disablement during Test: Where routine testing could actuate other systems (e.g. sprinklers, lifts), facilities must exist to disable outputs. This disablement (and its indication) must comply with BS EN 54-2.
Power Supply: Other systems should not normally draw power from the fire alarm. If unavoidable, demand must be calculated and supplied either by rated alarm PSU capacity or an ancillary PSU.
Accessibility: Interfaces must be installed in accessible locations for service. Housing them inside third-party enclosures (e.g. AHU panels) is discouraged unless service access is assured.
Monitoring: Connections between the fire alarm and external systems must be monitored for faults, in accordance with BS 7273 and BS 7346-8.
Fail-Safe Design: Outputs should default to a safe condition in the event of fault, loss of communication, or power failure.

Documentation

To meet BS 5839-1 requirements for system clarity and ongoing maintenance:

Interface Schedules: Document every I/O point, its location, and function.
Cause & Effect Matrix: Define logic clearly, ensuring outputs correspond with fire strategy.
As-Fitted Drawings: Show all interface wiring and modules.
Certificates: Modification or interface additions require appropriate certification (e.g. BS 5839-1 Annex G modification certificate).

Relevant Standards

BS 5839-1:2025 Clause 8 & Clause 11 - Actuation of other systems and monitoring of external circuits.
BS 7273 series - Operation of door release, smoke control, and suppression interfaces.
BS EN 54-2 - Disablement facilities and indication requirements.
BS 7346-8 / BS EN 12101 - Smoke and heat control systems.

Perfect — here’s a table you can drop straight into the Fire Alarms/Interfaces page, showing the BS 7273 parts most relevant to interfacing, with a short description of each. This keeps it aligned with BS 5839-1:2025 (Clause 8 explicitly points to BS 7273 for actuation of other systems).

BS 7273 Parts Relevant to Interfaces

Standard	Title	Application to Interfaces
BS 7273-1	Code of practice for operation of fire protection measures - Part 1: Electrical actuation of gaseous total flooding and local application extinguishing systems	Covers interface between fire alarm outputs and fixed gaseous suppression release equipment.
BS 7273-2	Code of practice for operation of fire protection measures - Part 2: Electrical actuation of sprinkler systems, water spray and foam systems	Guidance for interfacing with sprinkler flow/pressure switches, water mist, foam systems.
BS 7273-3	Specification for automatic release mechanisms for certain fire protection equipment	Focused on requirements for releasing devices (e.g. door holders, shutters) when actuated by fire alarm.
BS 7273-4	Code of practice for operation of fire protection measures - Part 4: Actuation of release mechanisms for doors	Critical for maglock, door holder, and access control release. Sets out categories A, B, C of compliance.
BS 7273-5	Code of practice for operation of fire protection measures - Part 5: Electrical actuation of fire dampers	Covers how fire alarm outputs should control motorised or fusible link dampers.
BS 7273-6	Code of practice for operation of fire protection measures - Part 6: Electrical actuation of smoke control systems	Defines how smoke extract fans, AOVs, dampers and pressurisation systems should be controlled and monitored by the fire alarm system.